<interactivity:Interaction.Triggers><!-- In order to Call Cleanup in ViewModel to unregister Messenger. --><interactivity:EventTriggerEventName="Unloaded"><interactivity:InvokeCommandActionCommand="{Binding ViewUnloadCommand}"/></interactivity:EventTrigger></interactivity:Interaction.Triggers>

Then my view will call the command in ViewModel to unregister the Messenger when this view is unloaded.

I've been working on a WPF project using this framework. Then I encountered this issue. I tried to search it on Google, MSDN and StackOverFlow. I found this solution when Messgener is used between ViewModel and View.
I would do something like this in CodeBehind file, to call Unregister in Unloaded event handler.

But when I am doing this in ViewModel, when I should call Unregister or Cleanup? Because I still need to receive this message again when it happens. But I don't want to receive this message multiple times
with just one shot.